The review addressed a clear question that was generally broadly defined in terms of the participants, intervention, outcomes and study design. Several relevant sources were searched but no attempts to minimise publication or language bias were reported. Methods were used to minimise reviewer error and bias in the assessment of validity and classification of interventions as compulsory or voluntary physical activity, but it is not clear whether similar steps were taken at the study selection stage and for the remainder of the data extraction. Validity was assessed, although only the composite score was presented; this makes it difficult to independently comment on the reliability of the evidence presented. In addition, it was not reported whether or not cluster RCTs had adjusted for correlation within clusters.
Adequate information about the included studies was presented in supplementary tables on the Public Health website (accessed 24/03/08; a subscription may be required for access). The narrative synthesis was appropriate in view of the diversity of the studies. The influence of various participant, intervention and study characteristics was assessed. However, the synthesis was limited to counting the numbers of effective and ineffective studies with each characteristic of interest. Hence, the conclusion regarding the decisive role of compulsory physical activity should perhaps be regarded more as hypotheses-generating rather than definitive.